Abstract
Spawning site conditions of endangered subspecies of Japanese sweetfish named Ryukyu-ayu inhabiting only in the Amami-Oshima Is., Southern Japan were evaluated with an in-situ measurement method of riverbed-scour potential to clarify substratum adhesion of riverbed. In the present method, man-made flow was occurred near river bed and the resultant scour depth was measured. The field survey using the present method was conducted in Yakugachigawa River in Amami-Oshima Is. The result shows that the present method was found to be more suitable for evaluating spawning site condition than a well-known penetrometer. The results also indicate that appropriate parameters for evaluation of spawning site conditions are discussed using scour depth, grain size and flow condition
